1. Field of the Invention
The present invention relates to a semiconductor device and a manufacturing method thereof.
In addition, the present invention relates to an object, a method, a method for producing an object, a process, a machine, manufacture, or a composition of matter. In particular, the present invention relates to, for example, a semiconductor device, a memory device, a display device, a liquid crystal display device, a light-emitting device, a driving method thereof, or a manufacturing method thereof. Alternatively, the present invention relates to, for example, an electronic device including the memory device, the display device, or the light-emitting device.
Note that in this specification, a semiconductor device refers to any device that can function by utilizing semiconductor characteristics, and an electro-optical device, a semiconductor circuit, an electronic device, and the like are all semiconductor devices.
2. Description of the Related Art
A technique by which a transistor is formed with a semiconductor film formed over a substrate having an insulating surface has been attracting attention. The transistor is applied to a wide range of semiconductor devices such as an integrated circuit and an image display device. A silicon film is widely known as a semiconductor film applicable to the transistor.
In the silicon film used as the semiconductor film of the transistor, amorphous silicon and crystalline silicon are used in accordance with the usage. For example, in the case of a transistor included in a large-sized display device, it is preferred to use an amorphous silicon film which can be formed using the established technique for forming a film in a large-sized area. On the other hand, in the case of a transistor included in a high-performance display device where driver circuits are formed over the same substrate, it is preferred to use a polycrystalline silicon film which can form a transistor having a high field-effect mobility. As a method for forming a polycrystalline silicon film, a heat treatment at a high temperature or a laser beam treatment which is performed on an amorphous silicon film has been known.
Further, in recent years, an oxide semiconductor film has attracted attention. For example, a transistor is disclosed in which an amorphous oxide semiconductor film containing indium, gallium, and zinc and having an electron carrier density of lower than 1018/cm3 is used (see Patent Document 1).
The oxide semiconductor film can be formed by a sputtering method and therefore can be applied to a transistor included in a large-sized display device. Moreover, a transistor including the oxide semiconductor film has a high field-effect mobility; therefore, a high-performance display device where driver circuits are formed over the same substrate can be obtained. Further, there is an advantage that capital investment can be reduced because part of production equipment for a transistor including an amorphous silicon film can be retrofitted and utilized.
In the case where glass is used as a substrate over which the transistor is provided, the electrical characteristics of the transistor might deteriorate due to diffusion of impurities from the glass. In order to suppress the deterioration, a film having a barrier property is provided between the substrate and the transistor.
[Reference]
[Patent Document 1] Japanese Published Patent Application No. 2006-165528